Cooperative distributed scheduling for device-to-device (D2D) communication

ABSTRACT

In a communication system having a plurality of user equipment (UE) devices that are operating in a contention based mode for device-to-device (D2D) communication, each UE device transmits a preferred transmission indicator when a condition for preferred transmission is met at the UE device. If a UE device receives a preferred transmission indicator, the UE device delays transmission of a D2D scheduling assignment (SA) to contend for communication resources for D2D communication. The length of the delay can be based on a number of preferred transmission indicators that are received. The preferred transmission indicator is based on a buffer size in one example.

CLAIM OF PRIORITY

The present application is a continuation of and claims priority to U.S.application Ser. No. 15/512,948, entitled “COOPERATIVE DISTRIBUTEDSCHEDULING FOR DEVICE-TO-DEVICE (D2D) COMMUNICATION” and filed on Mar.21, 2017, which is a national stage application of PCT/US2015/052188,entitled “COOPERATIVE DISTRIBUTED SCHEDULING FOR DEVICE-TO-DEVICE (D2D)COMMUNICATION” and filed on Sep. 25, 2015, which claims priority toProvisional Application No. 62/056,009 entitled “Cooperative DistributedScheduling for Mode 2 Network-assisted D2D,” filed Sep. 26, 2014, allassigned to the assignee hereof and hereby expressly incorporated byreference in their entirety.

FIELD

This invention generally relates to wireless communications and moreparticularly to cooperative distributed scheduling for device-to-device(D2D) communication between user equipment (UE) devices.

BACKGROUND

Many wireless communication systems use base stations to providegeographical service areas where wireless communication user equipment(UE) devices communicate with the base station (evolved Node B, eNB)providing the particular geographical service area in which the wirelesscommunication UE devices are located. The base stations are connectedwithin a network allowing communication links to be made between thewireless communication devices and other devices. In some situations,the communication links may be between UE devices within the servicearea of a base station. A cellular communication link between the UEdevices includes communication through the base station providing theservice. Where channel quality is sufficient, the UE devices cancommunicate directly through a device-to-device (D2D) communication linkthat does not include routing data through the base station.

In some situations, the D2D UE devices are assigned specificcommunication resources for D2D communication by an eNB. In somescenarios, the D2D UE devices select specific resources from a pool ofallocated resources for the D2D communication. In some systems, the UEdevices contend for the resources by randomly selecting resources froman allocated pool of resources and sending a control signal identifyingthe resources that will be used. If more than one UE device selects thesame resource, a collision occurs and the UE devices again attempt toselect resources for D2D communication. As the number of UE devices in ageographic area increases, the chances for collisions increases.

SUMMARY

In a communication system having a plurality of user equipment (UE)devices that are operating in a contention based mode fordevice-to-device (D2D) communication, each UE device transmits apreferred transmission indicator when a condition for preferredtransmission is met at the UE device. If a UE device receives apreferred transmission indicator, the UE device delays transmission of aD2D scheduling assignment (SA) to contend for communication resourcesfor D2D communication. The length of the delay can be based on a numberof preferred transmission indicators that are received. The preferredtransmission indicator is based on a buffer size in one example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of cellular communication system that supportsdevice-to-device (D2D) communication where a user equipment (UE) devicetransmits a preferred transmission indicator when a condition is metwhile operating in a resource contention mode and other UE devices, inresponse to receipt of the preferred transmission indicator, refrainfrom transmitting a scheduling assignment (SA) that contends for D2Dresources.

FIG. 2 is a block diagram of an example of a UE device suitable for useas one of the UE devices in FIG. 1 .

FIG. 3 is a block diagram of an example of a base station (eNB) suitablefor use as the base station (eNB) in FIG. 1 .

FIG. 4 is a flowchart of an example of a method of managing cooperativedistributed scheduling for device-to-device (D2D) communication.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of cellular communication system 100 thatsupports device-to-device (D2D) communication where a user equipment(UE) device transmits a preferred transmission indicator when acondition is met while operating in a resource contention mode and otherUE devices, in response to receipt of the preferred transmissionindicator, refrain from transmitting a scheduling assignment (SA) thatcontends for D2D resources. Although for the example of FIG. 1 the UEdevices receiving a preferred transmission indicator (PTI) refrain fromtransmitting the SA, a UE device receiving a PTI may transmit the SAwithout delay. Criteria can be established that allow UE devices tocontinue contention for resources without delay in a conventional mannerregardless of receipt of a PTI. In other words, the PTI is a requestthat may or may not be honored by UE devices receiving the PTI in somesituations.

A base station (eNB) 102 provides wireless communication services towireless communication user equipment (UE) devices within thegeographical service area 104, sometimes referred to as a cell. Severalbase stations are typically interconnected through a backhaul (notshown) to provide several service areas to cover large areas. Othersystem components forming system entities and performing systemfunctions such as Mobility Management Entity (MME), scheduling, gateway,and other functions are omitted from FIG. 1 in the interest of brevityand clarity. Any description with reference to FIG. 1 of the variousfunctions and operations of such equipment may be implemented in anynumber of devices, circuits, or elements. Two or more functional blocksmay be integrated in a single device, and the functions described asperformed in any single device may be implemented over several devicesin some circumstances. A cellular communication system is typicallyrequired to adhere to a communication standard or specification. TheThird-Generation Partnership Project Long-Term Evolution (3GPP LTE)communication specification is a specification for systems where basestations (eNodeBs) provide service to wireless communication devices(user equipment (UE) devices) using orthogonal frequency-divisionmultiplexing (OFDM) on the downlink and single-carrierfrequency-division multiple access (SC-FDMA) on the uplink. Although thetechniques described herein may be applied in other types ofcommunication systems, the exemplary systems discussed herein operate inaccordance with at least one revision of the 3GPP LTE communicationspecification.

The base station (eNB) 102 is a fixed transceiver station, sometimesreferred to as an evolved Node B, eNodeB or eNB, which may include acontroller in some circumstances. The base station 102 may be connectedto a controller through a backhaul which may include any combination ofwired, optical, and/or wireless communication channels. The controllermay include the functionality of the Mobility Management Entity (MME)and the Packet Gateway (P-GW) in a 3GPP LTE communication system.

Wireless (UE) communication devices (UE devices) 106-111 may be referredto as mobile devices, wireless devices, wireless communication devices,mobile wireless devices, user equipment, UEs, UE devices as well as byother terms. The UE devices 106-111 include electronics and code forcommunicating with base stations and with other wireless communicationdevices in D2D configurations. The UE devices may include devices suchas cell phones, personal digital assistants (PDAs), wireless modemcards, wireless modems, televisions with wireless communicationelectronics, and laptop and desktop computers as well as other devices.The combination of wireless communication electronics with an electronicdevice, therefore, may form a UE device 102, 104. For example, a UEdevice may include a wireless modem connected to an appliance, computer,or television.

The base station 102 includes a wireless transceiver that exchangeswireless signals with the UE devices when the UE device is within thecoverage area. Transmissions from the base stations and from the UEdevices 106-111 are governed by a communication specification thatdefines signaling, protocols, and parameters of the transmission. Thecommunication specification may provide strict rules for communicationand may also provide general requirements where specific implementationsmay vary while still adhering to the communication specification.Although the discussion below is directed to the 3GPP Long TermEvolution (LTE) communication specification, other communicationspecifications may be used in some circumstances. The communicationspecification defines at least a data channel and a control channel foruplink and downlink transmissions and specifies at least some timing andfrequency parameters for physical downlink control channels from a basestation to a UE device.

For the example of FIG. 1 , each of three UE devices 106, 107, 108 hasdata to transmit over a D2D link to another UE device 109, 110, 111.Although the UE devices may be within the coverage area, typically theUE devices are outside the coverage area when using the operating inMode 2 to acquire D2D resources. Each D2D communication link 112, 114,116 is a direct wireless communication link between a UE device and atleast one other UE device that does not route data through the basestation (eNB). For the example, all of the UE devices are operating in aresource contention mode for acquiring communication resources whereeach D2D UE device requiring communication resources for D2Dtransmission transmits a scheduling assignment (SA) message indicatingthe communication resources that it has selected for D2D transmission.An example of a resource contention mode is the Mode 2 used in systemsoperating in accordance with one or more revisions of the 3GPP LTEcommunication standard. In conventional systems using a resourcecontention mode, a collision may occur when multiple UE devices selectthe same communication resources and attempt to acquire those resourcesby indentifying them in an SA.

For the examples herein, however, collisions are avoided, or at leastminimized, by using a Cooperative Distributed Scheduling (CDS) techniquewhere a preferred transmission indicator (PTI) 118, 120 is transmittedfrom a UE device 106, 107 having data to transmit when a condition ismet at the UE device. As discussed below, the condition may at leastpartially be related to the buffer size at the UE device. UE devicesreceiving the preferred transmission indicator delay transmission oftheir SA and data in response to receiving the preferred transmissionindicator. The determination whether to delay and the length of thedelay may be based on factors such as the number of received preferredtransmission indicators and conditions at the UE device such as buffersize, required Quality of Service (QoS), and other factors.

Continuing with the example of FIG. 1 , a first transmitting UE device106, a second transmitting UE device 107, and a third transmitting UEdevice 108 have data to transmit over a D2D communication link 112, 114,116 to a first receiving UE device 109, a second receiving UE device 110and a third receiving UE device 111, respectively. All threetransmitting UE devices, therefore, have a buffer with some data.Although the example includes one to one device communications, the D2Dcommunication may include D2D groups including more than two UE devicesin some situations. The first transmitting UE device 106 and the secondtransmitting UE device transmit preferred transmission indicators 118,120 that are received by all of the transmitting UE devices in thisexample. Based on the conditions at the UE device and received preferredtransmission indicators, each transmitting UE device determines atransmission schedule.

In one example discussed in more detail with reference to FIG. 4 , theUE device determines the transmission schedule based its current buffersize, the number of received preferred transmission indicators, andwhether the next D2D transmission will reduce the buffer size below athreshold. For the example, each UE device transmits a single bit flagas a preferred transmission indicator when its buffer size is above athreshold and it will not be reduced below the threshold after the nexttransmission. The one bit flag is transmitted in the schedulingassignment (SA) and received by the other UE devices. The flag has oneof two values where an active value (e.g., bit set to 1) indicates thepreferred transmission indication. Each UE device determines the numberof received active value flags and refrains from transmitting the nextSA based on the number of active value flags and its transmission buffersize.

In some situations, the preferred transmission indicator 118, 120 isbased on the priority of the D2D call. For example, in public safety andemergency situations, a UE device may transmit the preferredtransmission indicator even if the buffered data is below the threshold.The system can be configured such that other UE devices not involved inpublic safety stop transmitting until the transmission preferenceindictor is no longer being transmitted as active.

In some circumstances, the preferred transmission indicator may be basedon the QoS of the transmission. For example, where the UE device istransmitting latency intolerant data such as real time voice and/orvideo, the UE device can transmit an active preferred transmissionindicator to increase the chances of obtaining the requiredcommunication resources.

Although a one bit flag is used for the example of FIG. 4 , the flag mayinclude more than one bit. Such an indicator may be useful where theindicator is based on multiple conditions. For example, if a preferredtransmission indicator is based on the buffer size, QoS and publicsafety criteria, a two bit flag can indicate no active flag (e.g.,value=00), low level transmission preference (e.g., value=01), mediumlevel transmission preference (e.g., value=10) or a high leveltransmission preference (e.g., value=11). The low level transmissionpreference may be transmitted when the buffer size is exceeded and themedium level transmission preference may be transmitted when a high QoSis required. The high level transmission preference may be transmittedfor public safety situations. Based on the flag value, other UE devicesmay delay transmissions or refrain from transmitting until the flagvalue decreases. A variety of combinations of thresholds and criteriacan be applied to determine whether the UE device refrains fromtransmitting and the length of the transmission delay.

FIG. 2 is a block diagram of an example of a UE device 200 suitable foruse as one of the UE devices 106-111 in FIG. 1 . The UE device 200includes a transceiver 202 and a controller 204, as well as othercomponents and circuitry (not shown) such as memory and a userinterface, for example.

The transceiver 202 includes a transmitter that transmits uplinkwireless signals to base stations (eNBs) and a receiver that receivesdownlink wireless signals from base stations (eNBs) over the uplink anddownlink channels, respectively. The transceiver 202 can also beconfigured to transmit and receive D2D signals using allocated cellularresources, such as uplink communication resources, for example. Thecontroller 204 controls components of the UE device 200 to manage thefunctions of the device 200 described herein as well as to facilitatethe overall functionality of the device 200. The controller 204 isconnected to the transceiver 202 and other components such as memory.

FIG. 3 is a block diagram of an example of a base station (eNB) 300suitable for use as the base station (eNB) 108 in FIG. 1 . The basestation (eNB) 300 includes a transceiver 302, a controller 304, and acommunication interface 306 as well as other components and circuitry(not shown) such as memory, for example.

The transceiver 302 exchanges wireless signals with the UE deviceswithin the service area 106. Transmissions from the base station (eNB)and from the UE devices are governed by a communication specificationthat defines signaling, protocols, and parameters of the transmission.The communication specification may provide strict rules forcommunication and may also provide general requirements where specificimplementations may vary while still adhering to the communicationspecification. Although the discussion herein is directed to the 3GPPLong Term Evolution (LTE) communication specification, othercommunication specifications may be used in some circumstances. Thecommunication specification defines at least a data channel and acontrol channel for uplink and downlink transmissions and specifies atleast some timing and frequency parameters for physical channels.

The transceiver 302, therefore, includes at least a downlink transmitterfor transmitting downlink signals and an uplink receiver for receivinguplink signals. The receiver and controller measure one or moreparameters to determine characteristics of the uplink channels. Anexample of a suitable technique includes determining CSI for thechannels.

For the example, the base station (eNB) 300 also includes acommunication interface 306 for facilitating communication over thebackhaul with other eNBs and network entities. Where X2 signaling isavailable, the communication interface 312 communicates over thebackhaul using X2.

FIG. 4 is a flowchart of an example of a method of managing cooperativedistributed scheduling for device-to-device (D2D) communication. For theexamples herein, the method is performed by executing code on thecontroller and utilizing other components of a UE device 200. The stepsof the method may be performed in a different order and some steps maybe performed simultaneously in some situations.

At step 402, the UE device is configured for Mode 2 transmission. Inaccordance with conventional systems using Mode 2 transmission, thereare two resource pools including one for transmission of SA and anotherfor data transmissions. Each pool has a different periodicity andredundancy. For example there are two SA resource pools and four Dataresource pools occurrences per period. The UE device transmits a datablock within a period. There are 4 occurrences within the period totransmit the data block. The data block is divided into 4 sub-packetswith the first sub-packet contains the source data sub-packet(systematic bits) and the other 3 contain the redundancy datasub-packets belonging to the data block. The same data block results in4 different sub-packets due to encoding. Each UE device randomly selectsa resource with the SA resource pool to transmit its SA. The same UEdevice selects another resource in the next SA resource pool toretransmit the SA. The same UE device then transmits data using foursub-packets by selecting four resources within each period. The dataresources selected by the UE device are indicated (pointed) by the SA.

At step 404, it is determined whether the UE device will engage in D2Dtransmission. The UE device determines if there is data to transmit overa D2D communication link. If the UE device will transmit over D2Dcommunication link, the procedure continues at step 406. Otherwise, theprocedure proceeds to step 408 where the UE device monitors D2Dtransmissions from other D2D UE devices.

At step 406, it is determined whether the size of the data buffer forthe D2D transmission is greater than or equal to a threshold. Thethreshold may be a pre-configured value or may be adjusted in somesituations. If the buffer is greater than or equal to the threshold, theprocedure continues at step 410. Otherwise, the procedure continues atstep 412.

At step 412, it is determined whether the UE device has received anyactive preferred transmission indicators (PTIs). For the example of FIG.4 , the active PTI is one bit flag of “1” indicating that the UE devicetransmitting the flag has a preferred transmission. If the UE device hasnot received any PTIs, the procedure continues at step 414 where the UEdevice transmits D2D using Mode 2 resources. Otherwise, the procedurecontinues at step 416 where the UE device delays D2D transmission basedon the number of active PTIs that have been received. For the exampleherein, the transmission of the SA and data are delayed by a number ofperiods equal to the number of active PTIs that were received by the UEdevice. The 3GPP specification defines a period for D2D communicationsand is referred to as Sidelink Period Communication or SL-PeriodComm.The period is configurable by the network and can have any of severallengths measured in subframes such as 40 subframes, 60 subframes, 70subframes, 80 subframes, 120 subframes, 140 subframes, 160 subframes,240 subframes, 280 subframes, and 320 subframes, for example. The PTI isset to inactive and the procedure returns to step 402 after the D2Dtransmission.

At step 410, it is determined whether the next D2D transmission willreduce the data buffer size below the threshold. If the next D2Dtransmission will reduce the buffer below the threshold, the procedurecontinues at step 418. Otherwise, the procedure continues at step 420.

A step 418, it is determined whether the UE device has received anyactive preferred transmission indicators (PTIs). If the UE device hasnot received any PTIs, the procedure continues at step 422. Otherwise,the procedure continues at step 424. At step 2.

At step 422, the UE device transmits D2D using Mode 2 resources and setsits PTI to inactive (e.g., flag of “0”). For the example, the UE devicetransmits an SA in the next period where the SA identifies the resourcesand includes the inactive PTI. The D2D data is then transmitted usingthe identified D2D resources and the procedure returns to step 406.

At step 424, the UE device transmits the D2D data in N retransmissions.For the example, the UE device transmits an SA and data in eachsubsequent period for N periods, where N is the number of active PTIsthat were received. The SAs include an active PTI for all transmissionsexcept the Nth retransmission where the PTI is set to inactive. Asdiscussed herein, a retransmission may include a transmission of theidentical block or it may include a new data block. For example, forVoIP scenarios, the UE device may drop the current packet and decide totransmit the next VoIP packet as the retransmission.

At step 420, it is determined whether the UE device has received anyactive preferred transmission indicators (PTIs). If the UE device hasnot received any PTIs, the procedure continues at step 426. Otherwise,the procedure continues at step 428.

At step 426, the UE device transmits D2D using Mode 2 resources and setsits PTI to active (e.g., flag of “1”). For the example, the UE devicetransmits an SA in the next period where the SA identifies the resourcesand includes the active PTI. The D2D data is then transmitted using theidentified D2D resources and the procedure returns to step 406.

At step 428, the UE device transmits the D2D data in N retransmissions.For the example, the UE device transmits an SA and data in eachsubsequent period for N periods, where N is the number of active PTIsthat were received. The SAs include an active PTI for all transmissions.Therefore, when it is determined that the next transmission will notreduce the buffer size below the threshold, the UE device retransmitsthe data for a number of retransmissions equal to the number of receivedactive PTIs and includes an active PTI for all retransmissions. If,however, the next transmission will reduce the size of the buffer belowthe threshold, the UE device retransmits the data for a number ofretransmissions equal to the number of received active PTIs and includesan active PTI for all retransmissions except the last.

Clearly, other embodiments and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. The above description is illustrative and not restrictive.This invention is to be limited only by the following claims, whichinclude all such embodiments and modifications when viewed inconjunction with the above specification and accompanying drawings. Thescope of the invention should, therefore, be determined not withreference to the above description, but instead should be determinedwith reference to the appended claims along with their full scope ofequivalents.

The invention claimed is:
 1. A method comprising: selecting, at a firstuser equipment (UE) device, a transmission preference level from aplurality of transmission preference levels, based on a Quality ofService (QoS) required by the first UE device for transmitting data overdirect communication, the plurality of transmission preference levelsincluding at least a low level, a medium level, and a high level; andtransmitting, from the first UE device to a second UE device, ascheduling assignment (SA) message including an indicator indicating theselected transmission preference level.
 2. The method of claim 1,wherein the indicator indicates the selected transmission preferencelevel with a plurality of bits.
 3. The method of claim 1, wherein theindicator indicates the selected transmission preference level with morethan two bits.
 4. A wireless communication user equipment (UE) devicecomprising: a controller configured to select a transmission preferencelevel from a plurality of transmission preference levels, based on aQuality of Service (QoS) required by the first UE device fortransmitting data over direct communication, the plurality oftransmission preference levels including at least a low level, a mediumlevel, and a high level; and a transmitter configured to transmit, to asecond UE device, a scheduling assignment (SA) message including anindicator indicating the selected transmission preference level.
 5. Thewireless communication UE device of claim 4, wherein the indicatorindicates the selected transmission preference level with a plurality ofbits.
 6. The wireless communication UE device of claim 4, wherein theindicator indicates the selected transmission preference level with morethan two bits.
 7. An apparatus for controlling a user equipment (UE)device, the apparatus comprising: a memory; and a processor, theprocessor configured to: select a transmission preference level from aplurality of transmission preference levels, based on a Quality ofService (QoS) required by a first UE device for transmitting data overdirect communication, the plurality of transmission preference levelsincluding at least a low level, a medium level, and a high level; andtransmit, to a second UE device, a scheduling assignment (SA) messageincluding an indicator indicating the selected transmission preferencelevel.
 8. The apparatus of claim 7, wherein the indicator indicates theselected transmission preference level with a plurality of bits.
 9. Theapparatus of claim 7, wherein the indicator indicates the selectedtransmission preference level with more than two bits.